Supercavitating medical probe and method of use

ABSTRACT

An electrosurgical working end that utilizes supercavitation phenomenon for controlled application of electrosurgical energy to tissue. In one preferred method of the invention, the system utilizes an electrosurgical surface that is rotatable in a liquid substance at very high surface velocities capable of localized lowering of the pressure of the substance below its saturated vapor pressure to cause supercavitation, and contemporaneously applying electrical energy from the electrosurgical surface across the cavity to ablate adjacent tissue. The system creates supercavitation with surface velocities of greater than about 70 m/sec in a liquid substance by means of high speed rotation and optionally ultrasound actuation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of Provisional U.S. Patent ApplicationSer. No. 60/636,352 filed Dec. 14, 2004 titled SupercavitatingElectrosurgical Device and Method of Use, and also claims benefit ofProvisional U.S. Patent Application Ser. No. 60/636,355 filed Dec. 14,2004 titled Supercavitating Medical Probe and Method of Use, both ofwhich are incorporated herein and made a part of the specification. Thisapplication is also a continuation-in-part of U.S. patent applicationSer. No. 11/065,180, filed Feb. 23, 2005 now U.S. Pat. No. 7,220,261,titled Electrical Discharge Devices and Techniques for MedicalProcedures which is a continuation of U.S. patent application Ser. No.10/282,555, filed Oct. 28, 2002 now U.S. Pat. No. 6,890,332 titledElectrical Discharge Devices and Techniques for Medical Procedures whichclaims benefit of Provisional U.S. Patent Application Ser. No.60/348,327 filed Oct. 27, 2001. U.S. patent application Ser. No.10/282,555 is also a continuation-in-part of U.S. patent applicationSer. No. 09/614,163 filed Jul. 11, 2000, now abandoned which is acontinuation-in-part of U.S. patent application Ser. No. 09/317,768filed May 24, 1999, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is related to instruments and techniques for controlledapplication of energy to tissue, and more particularly relates tosupercavitating surfaces and electrosurgical surfaces for ablatingtissue layers, for ablating holes in soft tissue and for ablatingocclusive materials, calculi and the like.

2. Description of the Related Art

Various electromagnetic and acoustic energy delivery sources have beeninvestigated for surgical tissue ablation or removal, includingradiofrequency (Rf) energy delivery, high intensity focused ultrasound(HIFU) tissue interactions and microwave energy absorption in tissue. Ingeneral, at high intensities, the above listed energy sources generatethermal effects that can vaporize tissue as the means of tissue ablationor removal. In other words, the energy sources elevate the temperatureof water in intra- and extracellular spaces to above 100° C. therebyexplosively vaporizing water to damage or destroy the tissue. Thedrawback to such purely thermally-mediated ablations is significantcollateral damage to tissue volumes adjacent to the targeted site. Whilein many surgical fields the above-described collateral thermal damagemay be acceptable, in fields in which thin layer ablations are requiredsuch as ophthalmology, neurology and interventional cardiology, there isa need to prevent, or limit, any such collateral damage.

Radiofrequency currents in tissue have been known for many years in theprior art for cutting a tissue mass or for coagulating regions within atissue mass. Conventional electrosurgical systems known in the artablate tissue by applying an electrical field across the targetedtissue. The actual energy-tissue interaction in Rf cutting is typicallydescribed in terms of a voltage differential that first boils a fluidand then causes a spark or arc across a vapor gap between an activeelectrode and the targeted site (e.g., coupled to a return electrode).Conventional electrosurgical ablation is generally achieved atfrequencies ranging from 500 kHz to 2.5 MHz, with power levels rangingfrom 75 to 750 W. In such prior art tissue cutting with Rf currents, thecurrent density rapidly decreases with distance from the exact energydeposition site on the tissue which is contacted by the spark. Still,the depth of tissue disruption and damage in such prior artelectrosurgical cutting may range from about 0.3 mm. to as much as 3.5mm. (see R. D. Tucker et al, Histologic characteristics ofelectrosurgical injuries, Journal Am. Assoc. Gynecol. Laparoscopy 4(2),pp. 201-206 1997.) The depth of tissue ablation depends on severalvariables, including (i) the conductivity of the tissue, (ii) theinsulative characteristics of the media in the physical gap between theactive electrode(s) and the tissue; (iii) the dimension of the physicalgap between the electrode(s) and the tissue; (iv) the power setting andoptional feedback control of the power level based upon electricalcharacteristics of the targeted tissue; (v) and the translation of theworking end relative to the tissue.

One prior art system in the field of electrosurgical ablation wasinvented by Eggers et al and is described as a Coblator™ (see. e.g.,disclosures of Eggers et al in U.S. Pat. Nos. 5,873,855; 5,888,198;5,891,095; 6,024,733; 6,032,674; 6,066,134 and the companion patentscited therein). The Coblator™ system relies on the creation of a voltagedifference between a plurality of closely spaced rod-like electrodeelements in a distal working end and a return electrode on theinstrument shaft. The Coblator™ system introduces an electricallyconductive fluid such as isotonic saline into the physical gaps about agroup of closely spaced active electrodes, and between the electrodegroup and the targeted tissue. The system applies electrical energy witha frequency of about 100 kHz and a voltage of about 100 to 300 V. TheCoblator™ promotional materials explain that at high voltage levels, theelectrically conductive fluid in the gaps between the closely spacedactive electrodes is converted to steam and then into a plasma. Thesupposition underlying the Coblator™ is that the actual energy-tissueinteraction produced by the system relates to charged particles in theplasma having sufficient energy to cause dissociation of molecular bondswithin tissue structures that come into contact with the plasma. Basedon this hypothesis, the accelerated charged particles have a very shortrange of travel, and the energy-tissue interaction causes moleculardissociation of tissue surfaces in contact with the plasma.

The types of ablation caused by conventional electrosurgical ablationand the ablation caused by the Coblator™ system share several commoncharacteristics. While conventional ablations and the Coblator™ablations are suitable for many procedures, both types of ablation arecaused by intense energy delivery that boils a fluid (or water intissue) to create an insulative steam layer which then is energized intoa plasma in an interface with tissue.

SUMMARY OF THE INVENTION

Cavitation is a phenomenon known to engineers in the field of fluiddynamics wherein small cavities of a partial vacuum form in a liquidsubstance wherein the cavities then rapidly collapse. In one example,cavitation occurs when water is forced to move at extremely high speed,e.g., in fluid flows around an obstacle such as a rapidly spinningpropeller. In such an example, the pressure of the fluid drops due toits high speed flows (Bemoulli's principle). When the pressure dropsbelow its saturated vapor pressure, its create a plurality of cavitiesin the water-hence the term cavitation. The cavities can take on anumber or forms and configurations that all consist of regions orbubbles of a partial vacuum, i.e., very low pressure gas phase water.

In conventional hydrodynamic terms, cavitation is an unintended andundesirable phenomenon. The regions of cavitation are transient as thecavities implode when the fluid flow velocities subside resulting in asudden rise in ambient pressure. The collapse of the cavities can causevery strong local shockwaves in the fluid, which may be audible and maydamage adjacent structures.

Supercavitation is a related phenomenon in which a partial vacuumenvelope is created by high speed fluid flows in a much larger andsustained manner than conventional cavitation to create a supercavity. Asupercavitating object's main features are a surface forms for inducingsuch cavitation—which often include flat surfaces and sharp, streamlinedand aqua- or aerodynamic edges which are believed to induce cavitation.When such surface features interact by traveling through, or rotatingin, a fluid at surface velocities in the range of 70 m/sec and higher,the liquid is displaced and thereby forced to move around the surfaceforms with such speeds that it creates an envelope of a partial vacuum.At suitable surface velocities, a sustainable supercavity can be formed.As used herein, the term supercavity is used to describe a cavity thatcan be sustained at least partially about a moving and/or oscillatingworking end surface of a medical probe.

In one example, the supercavitation phenomenon is used to allow objectsto travel under water at high speed. The Russian Shkval torpedoes may bethe only publicly known practical application of supercavitationtechnology. The supercavitating Shkval torpedo is believed to rotate athigh speed and more importantly has a rocket-powered high straight linevelocity. The torpedo body reportedly has faceted cavitators on its noseto induce a cavitation envelope that will extend to cover the entirebody when it reaches speeds in excess of about 150-200 km/h under water.Thereafter, the torpedo is no longer moving through water, but through asupercavity akin to air. The sustainable envelope or supercavity resultsin water wetting very little of the body's surface, thereby drasticallyreducing viscous drag. The drag reduction reportedly allows for torpedospeeds in excess of 500 km/h.

The present invention utilizes the supercavitation phenomenon in a novelmanner relating to application of electrosurgical energy to tissue. Inaccordance with a method of the invention, the system utilizes anelectrosurgical surface that is rotatable by a motor drive and/oractuatable by ultrasound in a liquid substance to create and confine anon-equilibrium supercavity proximate to, or in contact with, a site onbody structure targeted for ablation. The system includes means forapplying high frequency voltage to and across the supercavity whichresults in arcs of electrical energy across the supercavitation envelopeto thereby ablate the targeted site.

The present invention differs greatly from the prior art means describedabove for delivering ablative electrical energy to tissue. The inventionprovides a supercavity of a partial vacuum that is cold, and does nothave a thermal energy delivery component as in conventional Rf ablationor the Coblator™ system that thermally vaporizes saline and then appliesfurther energy to create an energetic plasma.

The invention provides a supercavitating electrode for ablation ofbiological material. The invention provides a method for biologicalmaterial removal that applies voltage about a supercavity induced byhigh velocity movement of an electrosurgical surface.

These and other objects and advantages of the present invention willbecome readily apparent upon further review of the following drawingsand specification.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to better understand the invention and to see how it may becarried out in practice, some preferred embodiments are next described,by way of non-limiting examples only, with reference to the accompanyingdrawings, in which like reference characters denote correspondingfeatures consistently throughout similar embodiments in the attacheddrawings.

FIG. 1 is a cut-away view of a working end of an exemplary probe of theinvention illustrating an electrosurgical working surface withsupercavitation occurring about the working surface for enablingapplication of electrosurgical energy across the cavity to tissue inclose proximity to the cavity.

FIG. 2A is a sectional view of an actuatable, rotatable member withsurface features for enabling supercavitation about the surface of theactuatable member.

FIG. 2B is a sectional view of a portion of a rotatable member similarto FIG. 2A with alternative surface features.

FIG. 2C is a sectional view of a portion of a rotatable member similarto FIGS. 2A-2B with alternative surface features.

FIG. 2D is a sectional view of a portion of a rotatable member similarto FIGS. 2A-2C with alternative surface features.

FIG. 3A is a cut-away view of a working end having a rotatable memberwith ultrahydrophobic surfaces.

FIG. 3B is an illustration of a fluid droplet on a non-ultrahydrophobicsurface.

FIG. 3C is a schematic illustration of an ultrahydrophobic surface ofdevice of FIG. 3A showing a very high contact angle.

FIG. 4 is a view of a method of practicing the principles of theinvention in ablating a bore in ocular tissue to treat ocularhypertension or glaucoma.

FIG. 5 is a cut-away view of another embodiment of working end with anactuatable member for creating supercavitation in a side port or recessin a sleeve member.

FIG. 6 is a cut-away view of another embodiment of working end with anactuatable member for creating supercavitation in a distal recessedportion of an elongate shaft.

FIG. 7 is a cut-away view of another embodiment of working end with anactuatable member for creating supercavitation wherein the working endincludes an aspiration source coupled to a flow channel in the workingend.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates an instrument system that comprises a medical probe100 with a distal portion shown in FIG. 1 that is configured forcreating cavitation and supercavitation about an actuatable or moveablesurface for controlling the application of electrosurgical energy totissue. In FIG. 1, an elongated shaft or sleeve member 102 carries anactuatable, moveable working end indicated at 105. In the embodiment ofFIG. 1, the actuatable working end 105 comprises an elongated rotatablemember 110 that extends through bore 112 in the shaft member 102 and isoperatively coupled to a motor drive described further below. Therotatable member 110 and working end 105 is rotatable at a very highspeed wherein the working surface 114 creates a cavity or supercavity115 that can substantially envelope the working end. In the embodimentof FIG. 1, it can be seen that the actuatable working end 105 is exposedto extend outwardly from open termination 118 of bore 112, but theworking end 105 can also be partly exposed in a side port of shaftmember 102 or can be recessed in an end port of the shaft member 102.The cross section of rotatable member 110 and working end 105 can rangebetween about 0.05 mm and 5.0 mm. In any embodiment, the working surface114 or electrosurgical surface 121 can have a shape that is rounded,blunt-tipped, tubular, sharp-tipped or bulbous-tipped.

The embodiment of FIG. 1 has an actuatable, rotatable working end 105that carries at least one electrode. More particularly, the working end105 of FIG. 1 comprises an electrosurgical energy delivery surface thatincludes first polarity electrode 120A and second opposing polarityelectrode 120B for operating in a bi-polar manner. The term bi-polar asused herein connotes that both polarity electrode surfaces are in closeproximity in the working end of the instrument. In another embodiment,the working end can carry a first polarity electrode 120A and the secondpolarity electrode can be located in shaft portion 102 or the secondpolarity electrode can comprise a ground pad to operate in a mono-polarmanner as is known in the art. In a typical embodiment of the invention,the actuatable working end 105 is configured for causing cavitation andincludes at least one electrode and is herein also termed anelectrosurgical surface 121. Such as electrosurgical surface 121 isoperatively connected to a high frequency voltage source and controllerindicated at 125. The proximal portion 126 of the rotatable member 110has an exterior insulator layer 128. In the embodiment of FIG. 1, thevoltage source 125 is connected to first and second insulated leads 130a and 130 b that extend through the interior of member 110 to respectiveelectrodes 120A and 120B. The coupling of electrical current to arotating member is accomplished by concentric rotating sleeve connectorsin a handle portion of the instrument as in known in the art.

In operation as depicted in FIG. 1, the working end 105 is immersed in aliquid substance 122 such as water, saline or blood. The liquidsubstance 122 is incompressible and rotation of the working end 105 inthe substance at a selected velocity is capable of causing microflowsabout working surface 114 and cavitation features 124 therein (furtherdescribed below) to cause localized reduction of the pressure of thesubstance 122 below its saturated vapor pressure to thereby create acavity 115 in the substance about the working surface 114. In order tocreate a cavity 115 that partially or completely surrounds the workingsurface 114, the surface 114 together with surface cavitation features124 are configured to achieve a relative surface speed in the liquidsubstance that exceeds about 70 m/sec. In one embodiment, the rotationdrive mechanism coupled to member 110 comprises an air turbine motor oran electric motor known in the art. In one embodiment, an air motor ofthe type used in dental instruments is used for the invention that canrotate at 100,000 rpm, 200,000 rpm or as high as 400,000 rpm to create asupercavity. The diameter of the rotatable element 110 can range fromabout 50 microns to about 5 mm and can achieve the surface speedsrequired to cause cavitation.

FIGS. 2A-2D illustrate exemplary features 124 for creating a cavity orsupercavity about a working surface 114 or electrosurgical surface 121,wherein the cavitation-inducing surface features comprise non-smoothsurfaces. For example, FIG. 2A illustrates a rotatable member 110 thattransitions from a smooth surface into a working surface 114 includingflattened facets 131 with edges 132 that can induce partial cavitationand supercavitation. The rotatable member 110 is indicated as having apositive polarity for cooperating with a negative polarity electrodelocated elsewhere in the working end or in a ground pad. In FIG. 2B, therotatable member 110 carries a plurality of microblades or protrusions133 that can be any pitch (spiral lead) similar to that suggested inFIG. 1. The member 110 carries spaced apart conductive coatings thatcomprise opposing polarity electrodes 120A and 120B. FIG. 2B illustratesthe electrical field EF or configuration of current flow that can becreated about surface 114. In FIG. 2C, the rotatable member 110 carriesblades 135 that extend in a suitable arcuate shape and form. FIG. 2Dillustrates a tubular spinnable element 110 with grooves 136 andinterior bore 138 that also can extend to vents 139 in the surface 114.In the embodiment of FIG. 2D, concentric interior and exterior layerscomprise opposing polarity electrodes 120A and 120B with insulator layer140 therebetween. All of the above geometries it is believed can beconfigured for causing supercavitation in a liquid substance 122 about aworking surface 114 at a selected surface rotation speed in the range of70 m/sec and higher, and in some cases in the range of 10 m/sec andhigher.

In another embodiment, FIG. 3A illustrates an electrosurgical electrodehaving ultrahydrophobic surface features which it is believed willassist in creating supercavitation about an actuatable or moveablesurface 114. As depicted in FIG. 3B, an ultrahydrophobic electrodesurface indicated at 142 is profiled with microscopic structures 144having nearly vertical side walls, wherein an aqueous fluid becomessupported by the tips of the structures 144 due to negative capillaryeffect. FIG. 3B illustrates a water droplet having a very high contactangle and low sliding resistance (small contact angle hysteresis) onsuch a surface. For example, the contact angle is above about 105°. Insmall cross section rotatable members 110, it is believed that theultrahydrophobic surfaces will reduce drag by a significant amount thusresulting in a thin cavity about the surface. The surface also functionsas an electrosurgical surface. The invention encompasses asupercavitating electrosurgical surface wherein the surface has featuresthat assist in developing a supercavity under high speed rotation oroscillation (or both) in a liquid substance 122. The invention furtheralso encompasses any ultrahydrophobic surface electrode whether in anon-cavitating or supercavitating electrosurgical surface.

As can be seen in FIGS. 1 and 3A, the system optionally includes a fluidsource 145 that allows inflows of a fluid media M into an interface withtargeted tissue, for example through bore 112 or another fluid channelin rotatable member 110. FIG. 2B further illustrates an electrical fieldEF between the first and second electrodes carried by the rotatableelement 110. In FIG. 2B, it can be seen that the electrosurgical surface121 carries first and second electrodes 120A and 120B in spaced apartaxial electrode surfaces with insulator portion 140 therebetween. In analternative embodiment (not shown), the first and second electrodes 120Aand 120B can be configured in an axially spaced apart arrangement onrotatable element 110. In such embodiments, the cross-section ranging ofelement 110 can range from about 100 microns to about 5 mm. Theinvention encompasses any mono-polar or bipolar arrangement of first andsecond opposing polarity electrodes 120A and 120B, or a plurality spacedapart opposing polarity electrodes 120A and 120B in any axial, helicalor angular arrangement.

In FIG. 4, the method of the invention is depicted schematically inablating a bore 150 in ocular tissue between a region carrying the eye'slymphatic network 152 through the sclera 154 to a selected region of theciliary body 156. The creation of a bore 150 can be effective intreating ocular hypertension, using outflows through the lymphaticnetwork in a subconjunctival region 160 as generally described in theauthor's co-pending U.S. patent application Ser. No. 10/759,797 filedJan. 17, 2004 which is incorporated herein by this reference. Intreating ocular hypertension, the bore 150 in tissue, or a plurality ofbores, preferably has a diameter ranging from about 50 microns to 250microns. Thus, the cross section of the rotatable member 110 as in FIG.1 can be in this range.

The method of the invention thus comprises: (a) causing a selected rateof relative motion between a liquid substance 122 and a working surfaceor electrosurgical surface to create a partial cavity or a supercavity,and (b) applying electrical energy across the cavity in close proximityto mammalian body structure to apply ablative energy to the bodystructure. The method includes translating the electrosurgical surfaceto ablate a surface region of body structure, or axially moving theelectrosurgical surface to ablate a hole in the body structure. Invarious embodiments, the apparatus of the invention is configured with aworking end capable of creating a supercavity around at least a portionof an electrosurgical surface. In another embodiment, the working endcreates a cavity that surrounds both first and second polarityelectrodes. The method of the invention includes immersing an actuatableworking surface in a liquid substance, providing a rate of motion in theworking surface capable of localized lowering of the pressure of thesubstance below the saturated vapor pressure to create a cavity therein,and contemporaneously delivering electrical energy across the cavity totissue. The method of the invention includes immersing an actuatableworking surface in a liquid substance, providing a rate of motion in animmersed working surface that causes localized increase of the impedanceof the substance by a factor of at least one hundred, or at least onethousand. The increase in impedance results from the cavity or vaporousform of the low pressure media which in turn results in an insulativegap that electrical energy arcs across to apply energy to tissue.

In another working end embodiment 105 depicted in FIG. 5, a rotatablemember 110 has an exposed working surface 114 in a window or port 160 inan elongated shaft member 102. An embodiment in the configuration ofFIG. 5 can be used to create a localized supercavity 115 in a selectedangular region for ablating a side of a body lumen such as in a TURPprocedure or in the ablation of endoluminal occlusive material. Thefirst polarity electrode 120A can be a portion of rotatable element 110as depicted in FIG. 5. In this embodiment, the second opposing polarityelectrode can be spaced apart on an opposing portion of rotatable member110 or on the shaft member 102, or a combination thereof. In anothersimilar embodiment, a working end 105 as in FIG. 5 can be carried at thedistal end of an elongated flexible catheter configured for endoluminalnavigation. The cavitation inducing surface 114 also can be flexiblemember, for example as used in a cutting loop used in a TURP procedure.

In another embodiment, the apparatus of the invention comprise a workingend 105 that carries an elongated actuatable member 110 (similar to FIG.6) coupled to an ultrasound source, such as one or more piezoelectricelements. The ultrasound source is configured for oscillating theworking surface 114 at a rate capable of localized lowering of thepressure of a surrounding liquid substance to below its saturated vaporpressure to create a cavity therein. In one embodiment, the workingsurface is actuatable in rotation as described above and is alsoactuatable by ultrasound to achieve surface speeds of 70 m/sec or moreto thereby lower the pressure of liquid substance to below its saturatedvapor pressure to thereby create a cavity therein. In these embodiments,the method of the invention again contemporaneously delivers electricalenergy across the supercavity to body structure adjacent the working endAs shown, the working end 105 includes with an actuatable member 110 forcreating supercavitation in a distal recessed portion 170 of an elongateshaft 102.

In another embodiment depicted in FIG. 7, the apparatus of the inventionfurther includes an aspiration source 165 for aspirating fluid andablation debris from the targeted site. The aspiration source is coupledto an open-ended channel 138 extend through the center of a tubularrotating member 110 as in FIG. 2D, or the aspiration means can becoupled to bore 112 in which the member 110 rotates (see FIG. 1). Inanother embodiment, the working end includes a cavitation-inducingsurface 114 that is adjustable in extension from the distal end of shaftmember 102 to provide different cavity dimensions.

In one embodiment of the invention depicted in FIG. 7, the system isconfigured with a de-mateable, disposable shaft 102 and working end 105that is coupled handle portion 182 that carries the motor drive. Such adevice can be dimensioned for use in arthroscopic procedures to treatand ablate a targeted site within a joint.

In any embodiment, the system includes a computer controller operativelyconnected to the high frequency electrical energy source 125 to controldelivery of electrical delivery. In one embodiment, the system andcontroller include an electrode arrangement for sensing impedance acrossa supercavity 115 as in FIG. 1 to initiate, modulate or terminate energydelivery. The controller also can modulate energy delivery upon sensinga selected rate of rotation or oscillation. The controller also canmodulate a pulsed energy delivery repetition rate. Alternatively, anysort of on-off switch in a foot pedal or hand switch can be used toactuate the voltage source and controller 125 when using operating thesystem.

The cavitation-enabled electrosurgical surfaces and methods above havebeen described in connection with several surgical procedures forvolumetric tissue removal, such as in ablating a hole in scleral tissueto treat glaucoma (FIG. 4) and in tissue ablation in TURP procedures. Itwill be clear to those having skill in the art that the system hasoperational characteristics that may be suitable for a wide range ofvolumetric tissue removal procedures in, or on, structure of a mammalianbody. For example, the system has other uses in ophthalmology such as incutting retinal tissue, cutting a lens capsule in capsularhexisprocedures, or fracturing and aspirating a lens nucleus in a cataractprocedure. The system and method of the invention are suitable forarthroscopic surgeries, including partial meniscectomies, synovectonies,chondroplasties, tendon and cartilage removals, and in generalresurfacing and texturing of cartilage, tendon and bone surfaces. Inaddition, in the ENT and GI fields, there are a variety of proceduresthat require volumetric tissue removal either at a tissue surface or atthe end of a probe inserted percutaneously in treating nose and throatdisorders, for example, soft palate volume reduction surgery, turbinatereduction surgery, sinus surgery and jaw bone surgery. The system can beused in skin resurfacing with a thin layer of fluid or gel placed overthe skin. The system also can be used in spine surgery and neurosurgeryin which collateral thermal damage can be prevented. These proceduresrequire that the surgeon be provided with means to remove tissue inclose proximity to delicate structures and nerves that cannot bedamaged, which procedures lend themselves to the methods disclosedherein.

In many surgical fields, the selective removal of malignant tissue orother tumors may be accomplished by the present invention, such as inbreast tumors or liver tumors. For example, a form ofstereotactic-directed probe may be used to ablate breast lesions. Theuse of the system in tumor ablation and removal is assisted by the factthat a supercavitation is viewable under ultrasound imaging forcontrolling margins of ablation.

The method of the invention also may have use in interventionalcardiology to remove vascular occlusions or in CTO procedures to ablatea hole in a calcified cap of a chronic total occlusion. The method ofthe invention also may be useful for drilling holes in tissue such as inTMR procedures (transmyocardial revascularization). The material removalmethods described above apply to all body structures, which includeaccretions, calculi and the like.

Those skilled in the art will appreciate that the exemplary embodimentsand descriptions thereof are merely illustrative of the invention as awhole, and that variations in controlling the duration of intervals ofenergy delivery, in controlling the repetition rate, and in controllingthe voltage applied to create the interval of intense electric fieldsmay be made within the spirit and scope of the invention. Specificfeatures of the invention may be shown in some figures and not inothers, and this is for convenience only and any feature may be combinedwith another in accordance with the invention. While the principles ofthe invention have been made clear in the exemplary embodiments, it willbe obvious to those skilled in the art that modifications of thestructure, arrangement, proportions, elements, and materials may beutilized in the practice of the invention, and otherwise, which areparticularly adapted to specific environments and operative requirementswithout departing from the principles of the invention. Particularfeatures that are presented in dependent claims can be combined and fallwithin the scope of the invention. The invention also encompassesembodiments as if dependent claims were alternatively written in amultiple dependent claim format with reference to other independentclaims.

What is claimed is:
 1. An electrosurgical method for applying electricalenergy to body structure comprising: (a) immersing an electrosurgicalsurface in a liquid substance, (b) providing a rate of motion in theelectrosurgical surface capable of localized lowering of the pressure ofthe substance below the saturated vapor pressure thereof to create acavity; and (c) applying the electrical energy from the electrosurgicalsurface across the cavity in close proximity to mammalian body structurethereby applying the electrical energy to the body structure.
 2. Theelectrosurgical method of claim 1 including providing the rate of motionof at least 70 m/sec.
 3. The electrosurgical method of claim 1 includingproviding the rate of motion by at least one of rotation of theelectrosurgical surface and ultrasonic actuation of the electrosurgicalsurface.
 4. The electrosurgical method of claim 1 wherein step (c)ablates a portion of the body structure.
 5. The electrosurgical methodof claim 4 further comprising translating the electrosurgical surface toapply the electrical energy to a surface portion of the body structure.6. The electrosurgical method of claim 4 further comprising penetratingthe electrosurgical surface into a tissue of the mammalian bodystructure to ablate a path in the tissue.
 7. The electrosurgical methodof claim 1 wherein the applying of the electrical energy across thecavity is carried out between first and second opposing polarityportions of the electrosurgical surface.
 8. The electrosurgical methodof claim 1 wherein the applying of the electrical energy across thecavity is carried out between a first polarity of the electrosurgicalsurface and a second polarity of a ground pad.
 9. An electrosurgicalmethod for applying electrical energy to body structure comprising: (a)immersing a working end including a moveable working surface in a liquidsubstance, (b) providing a rate of motion in the working surface capableof localized lowering of the pressure of the substance below thesaturated vapor pressure thereof to create a cavity; and (c) applyingthe electrical energy across the cavity in close proximity to mammalianbody structure thereby applying the electrical energy to said bodystructure.
 10. The electrosurgical method of claim 9 wherein providingthe rate of motion in the working surface causes localized increase ofthe impedance of the substance by a factor of at least one hundred. 11.The electrosurgical method of claim 9 wherein providing the rate ofmotion in the working surface causes localized increase of the impedanceof the substance by a factor of at least one thousand.
 12. Theelectrosurgical method of claim 9 wherein the applying of the electricalenergy across the cavity is carried by at least one electrode in theworking end.
 13. The electrosurgical method of claim 9 wherein theapplying of the electrical energy across the cavity is carried by atleast one electrode in the working surface.